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<br />The ':i1JL)~Jear fl ood even t is importdnt in mak i ng the pub 1 ie aware tha t floods
<br />larger than the lOCi-year floOd can and dO occur. The SUU-year tload event
<br />c<ln also be used for regulating high risk developments within the flood-
<br />plain.
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<br />I ~~TrR~RfTATI 011 AN!). _U.~E_j!LIlIf>..ORT._ O~T~
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<br />fLOUU H{~l{\!.~N_~Y AI!ll..J:!l::.CIiAfM
<br />TllelU-, 50-.1lJO-,dnd5lJO-yearflootleventswereusedastnetloOClfrequell_
<br />c i e 5 for tll i s f1 ood pia i n ana 1 y, is. Thu s, the dd ta dev e 1 opeO i n th i s rt~ port
<br />will be compHible not only for regulation purposes and State of Coloraco
<br />H.ll. 1iJ41 designations, but also for Federal Insurance Administration flood
<br />insurance rate studies.
<br />
<br />Tnese vdrious flood
<br />of years indicated.
<br />once in d ]OO-year
<br />
<br />events have an average <!Ccurr~rI~~ of once in the nwnoer
<br />For example, tn~ WO-year flood occurs (on the average)
<br />period and has a one percent chance of oeing equaled or
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<br />Flooded Area
<br />The WU-yearfrequency flood has tleen selected by tni' State of Colorado ilS
<br />the flood event to be used for floodplain aelineation and reguliltion. Since
<br />the bdse map for the Fl (loded Ar~a plates is a conto~r map, the outl ines of
<br />other floods can be readily plotted using infonnation in Table 3.
<br />
<br />ex~eeded in any given year.
<br />
<br />The area delineated on the flooded area sheets as the lUU-year flooap1ain
<br />meetstherequirernentsofH.B.1IJ4l as an area of Stale interest. AlSO,upon
<br />official approval of this report by the ColoradO '.later Con,ervation Board.
<br />the area outllnedby the lOU-year flood boundary can be designated a flood.
<br />pl ain are~ and may be regYlilteil accordingly by the local official,.
<br />
<br />The particYlaruses of the v,lrioys flood events, in dddition to those stdted
<br />dbove, are listed below.
<br />
<br />I ntormati on regardi ng tile lO~year and 5U.yedr frequency fl ood~ is espec i a 11 y
<br />useful forfutyreengineering studies and land-use planning purposes related
<br />to minor road systems. minor channel improvemE'nts. and appurtenant ,truc-
<br />ti.iroos. For str~ct~n,~ ~nd uses ur this typ!: on t,,~ srlld,l",r tributdries, dnd
<br />in areas where the high risk of stryctural failure is &onomically fedsible
<br />dnd the hazard to 1 i foo dnd property none~ lstent, the use of the lower
<br />frequency flOOdS may DC conSlaercd.
<br />
<br />ShallOW Flooding
<br />On several Mthe flooded dredr.k1pS in this report. arCdS subjE'ct tu "$h<lllow
<br />Flooding Kyaraulical1y Disconnected from the !,aln Channel" h"ve neen
<br />dclineJted. In the.e area, flooding is generally les,; than +1.~ feN in
<br />depth dnd lS due to flows ledving the Channel up,;tream dnd following the
<br />terrain of tIle lJnd. '~Jter surface elcv~tions in the,e areas are generdlly
<br />hi gher than tile e\ev~tions tor nodi n Chdnnel flow. AI though the,e areas dre
<br />generdlly lo~ hdZdrd areas, development shoyld be permi tted only after iI
<br />detailed site investigation of potential flowdepthsdndflowpatterns,
<br />
<br />The lOLl-yeM flOOd ~vent ,"dY dlso be used for enginGGring design purposes
<br />where a lower riSk of tai 1 ure than the lO-yedr or ~O-y~ar flood is de,irea.
<br />Kowever, the most importdnt use of the lOO-year flood event lies in floOd-
<br />plain designdtion dnll land-use reguldtionas set torth in the Stat estatutes.
<br />The State of Colorddo considers the lUU-year frequency tlooo dS the flOOd
<br />event to be used in designing dnd protecting structures and d...ellings for
<br />hU'Hdnoccllpdtion. Therefor>'!. floOdpldin regulations dreoasea upon tnel(Ju-
<br />yeJr flood. Also, the drea which would be inundatetl by the \Ov-year flOOd
<br />,nay I)", LI>'!lil'e<1l",d d' drl dr'ed 0f o:,t4t~ intnc,t dS sd cortn ln H.~. lu41.
<br />
<br />FlOOd Elevations
<br />The flOOd frequency elevdtion dnd discharge data t:lble, Tabl e 3, lists t~e
<br />lU_, 5U-. 1 GU., dnd SOli-yedr flood el eVdtions dt s,'lecte~ reft'rence poi nt,.
<br />The t I 00(1ed arbl <;h,~~ts y i v~ the pI dn vie... of the floolled ared on d COli toLlr
<br />lJase IIIdp an,! the hi ~h water el eVdti on~ for the lULI-y""r floOd ",on De lnter_
<br />po 1 :lted from th is. ,\1 so. the cross ~ecti on fi 'lures ~~lOW a gr~phi r.a 1 repre-
<br />sentHion cf the high w~ter elevations at ty~ical valley cro:JS, sectio~~
<br />throughoutthestu<1yreach.
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